Adds structured docs for variable declarations.

- adds natspec generation for state variables.
- exports structured docs for state variables to JSON.

libsolidity/ast/AST.h

@@ -859,7 +859,7 @@ private:
  * Declaration of a variable. This can be used in various places, e.g. in function parameter
  * lists, struct definitions and even function bodies.
  */
-class VariableDeclaration: public Declaration
+class VariableDeclaration: public Declaration, public StructurallyDocumented
 {
 public:
 	enum Location { Unspecified, Storage, Memory, CallData };
@@ -882,6 +882,7 @@ public:
 		ASTPointer<ASTString> const& _name,
 		ASTPointer<Expression> _value,
 		Visibility _visibility,
+        ASTPointer<StructuredDocumentation> const& _documentation,
 		bool _isStateVar = false,
 		bool _isIndexed = false,
 		Mutability _mutability = Mutability::Mutable,
@@ -889,8 +890,9 @@ public:
 		Location _referenceLocation = Location::Unspecified
 	):
 		Declaration(_id, _location, _name, _visibility),
-		m_typeName(std::move(_type)),
-		m_value(std::move(_value)),
+        StructurallyDocumented(_documentation),
+		m_typeName(_type),
+		m_value(_value),
 		m_isStateVariable(_isStateVar),
 		m_isIndexed(_isIndexed),
 		m_mutability(_mutability),

libsolidity/ast/ASTAnnotations.h

@@ -171,7 +171,7 @@ struct ModifierDefinitionAnnotation: CallableDeclarationAnnotation, Structurally
 {
 };
 
-struct VariableDeclarationAnnotation: DeclarationAnnotation
+struct VariableDeclarationAnnotation: DeclarationAnnotation, StructurallyDocumentedAnnotation
 {
 	/// Type of variable (type of identifier referencing this variable).
 	TypePointer type = nullptr;

libsolidity/ast/ASTJsonConverter.cpp

@@ -390,7 +390,10 @@ bool ASTJsonConverter::visit(VariableDeclaration const& _node)
 		make_pair("typeDescriptions", typePointerToJson(_node.annotation().type, true))
 	};
 	if (_node.isStateVariable() && _node.isPublic())
+	{
 		attributes.emplace_back("functionSelector", _node.externalIdentifierHex());
+		attributes.emplace_back("documentation", _node.documentation() ? toJson(*_node.documentation()) : Json::nullValue);
+	}
 	if (m_inEvent)
 		attributes.emplace_back("indexed", _node.isIndexed());
 	if (!_node.annotation().baseFunctions.empty())

libsolidity/ast/ASTJsonImporter.cpp

@@ -441,6 +441,7 @@ ASTPointer<VariableDeclaration> ASTJsonImporter::createVariableDeclaration(Json:
 		make_shared<ASTString>(member(_node, "name").asString()),
 		nullOrCast<Expression>(member(_node, "value")),
 		visibility(_node),
+        _node["documentation"].isNull() ? nullptr : createDocumentation(member(_node, "documentation")),
 		memberAsBool(_node, "stateVariable"),
 		_node.isMember("indexed") ? memberAsBool(_node, "indexed") : false,
 		mutability,